1. Field of the Invention
The present invention relates to a hybrid power system that gasifies fuel in a gasifying furnace and drives a turbine by using combustion gas generated by burning mixed gas of the gas generated in the gasifying furnace and compressed air in a gas turbine, to generate power, and boosts compressed air bled from a compressor in the gas turbine to feed the compressed air to the gasifying furnace, and a method of operating the hybrid power system.
2. Description of the Related Art
For example, a gas turbine includes a compressor, a combustor, and a turbine, in which air taken in from an air inlet port is compressed by the compressor so that compressed air with high temperature and high pressure is generated, fuel is supplied to the combustion air to be burned in the combustor, the turbine is driven by thus generated combustion gas with high temperature and high pressure, and a power generator coupled to the turbine is driven to generate power. In a hybrid power plant in which a gasifying furnace is applied to such a gas turbine, solid fuel or liquid fuel is gasified in the gasifying furnace, gas generated in the gasifying furnace is supplied to a gas turbine to be mixed with compressed air, the turbine is driven by combustion gas generated by burning the mixed gas, exhaust gas with high temperature exhausted from the gas turbine is fed to a boiler to generate steam, and generated steam is fed to a steam turbine to drive a generator and to generate power.
In such a hybrid power plant, unburned gas is generated by supplying pulverized coal (coal) as fuel, oxygen, and nitrogen in the gasifying furnace to cause imperfect combustion, and gas for combustion used in the gas turbine is purified from the unburned gas in the gasifying furnace. Compressed air for conveyance is supplied to the gasifying furnace, and unburned gas generated from the compressed air is fed to a gas purifying apparatus or the gas turbine. In a conventional hybrid power plant, compressed air bled from the compressor in the gas turbine is boosted by a booster to be fed to the gasifying furnace.
In this case, since gas for combustion cannot be immediately generated in the gasifying furnace at an activation time of the hybrid power plant, liquid fuel is supplied to the combustor instead of coal gas to activate the gas turbine. At this time, a bleed source valve provided in a bleed line extending to the booster from the compressor in the gas turbine is in a closed state. When gas for combustion is made producible in the gasifying furnace, the bleed source valve is opened to boost bled air from the compressor by the combustor and supply the same to the gasifying furnace, and coal gas is supplied to the combustor by the boosted gas to drive the gas turbine.
Japanese Patent Application Laid-Open No. H05-248260 discloses this type of hybrid power plant.
As described above, the bleed source valve is provided in the bleed line connecting the compressor in the gas turbine and the booster in the hybrid power plant, and the bleed source valve is maintained in an opened state at an activation time of the gasifying furnace. However, although the bleed source valve can be activated by hydraulic pressure, air pressure, electromagnetic force, or the like, when oil pressure leakage, air pressure leakage, or electric breakdown occurs, the bleed source valve is closed, so that surging occurs without feeding bled air to the booster, which possibly damages the booster. Therefore, when the bleed source valve is closed due to breakdown, the gas turbine and the booster are stopped immediately and the gasifying furnace is also stopped.
However, when the bleed source valve is gradually closed due to breakdown, although the gas turbine and the booster are simultaneously stopped, the booster cannot be stopped immediately due to its inertial force and a boosting operation of bled air continues by a predetermined time. On the other hand, since pressure in a casing lowers due to stoppage of the compressor in the gas turbine, compressed air of the compressor is not supplied to the booster, which causes surging in the compressor.